The disclosure relates to a solenoid device having a magnet armature and an armature counterpiece which is arranged at the end of the magnet armature, wherein the magnet armature and armature counterpiece can be moved in relation to one another, and an air gap, via which a magnetic series connection of the solenoid device is present, is provided between a magnet armature end and an armature counterpiece end.
Solenoid devices of the type mentioned at the beginning are known from the prior art. They may be embodied, for example, component of solenoid valves or in each case as a solenoid valve, wherein the solenoid valves can in turn be used for driver assistance devices, in particular ABS, TCS or ESP devices. The solenoid device has the magnet armature which can be moved in relation to the armature counterpiece. In this context, frequently only the magnet armature can be moved, while the armature counterpiece is arranged in a positionally fixed fashion. The armature counterpiece may be embodied, for example, as a pole core. In order to bring about the relative movement of the magnet armature and armature counterpiece, the two elements interact. For this purpose, for example the armature counterpiece has one or more coils, while the magnet armature is composed of a magnetizable or magnetic material. The armature counterpiece is provided at the end of the magnet armature. The magnet armature and the armature counterpiece are usually arranged with respect to one another in such a way that they cannot be connected to one another, irrespective of the movement of the magnet armature and armature counterpiece in relation to one another. Accordingly, between the magnet armature the armature counterpiece or the end of the magnet armature which faces the armature counterpiece and the end of the armature counterpiece which faces the magnet armature, that is to say the magnet armature end and the armature counterpiece end, there is a gap, referred to as the air gap or working air gap. The size of the air gap is dependent on the position of the magnet armature in relation to the armature counterpiece. The size of the air gap accordingly changes when the magnet armature and armature counterpiece move in relation to one another. The term air gap does not mean that the gap which is present between the magnet armature end the armature counterpiece end is actually filled with air. Instead, the gap can be filled with any desired media and serves only for spacing apart the magnet armature and the armature counterpiece.
The magnet armature and the armature counterpiece together form an actuating device. The magnetic force which can be generated by this actuating device and which implements the movement of the magnet armature and armature counterpiece in relation to one another is characterized by the size of the air gap. This means that the magnetic force is dependent on the size of the air gap, wherein as the air gap becomes smaller the magnetic force usually increases very strongly, usually exponentially. This strong increase as the air gap becomes smaller makes continuous adjustability or the proportionalization of the solenoid device more difficult.
It is known that this strong increase in the magnetic force can be at least partially remedied by enlarging the air gap. This is due to the fact that the actuating force or magnetic force which can be implemented with the solenoid device, and which ensures that the relative movement of the magnet armature and the armature counterpiece occurs, is involved/decreases exponentially as the air gap grows. The profile of the magnetic force plotted against the size of the air gap therefore becomes flatter as the air gap becomes larger, but is at the same time at a relatively low level. However, this low level of the magnetic force is problematic without the possibility of geometrically increasing relevant parts of the solenoid device, in particular the at least one coil. This applies, in particular, when the solenoid device is used for a solenoid valve which is closed in the currentless state. Here, the available magnetic force must be sufficiently large to open the solenoid valve counter to a compression spring which acts in a closing fashion. The compression spring is usually embodied in such a strong way that it even in a slightly prestressed state it can overcome the opening force brought about by the operating medium of the solenoid valve or by the pressure difference across the solenoid valve. A very stiff compression spring is also necessary as a result of the enlargement of the air gap because the gradients of the spring force and of the magnetic force plotted against the difference of the magnetic armature and armature counterpiece should be matched to one another. In this context, the gradient of the spring force is frequently selected to be larger than the gradient of the magnetic force.
A further possible way of at least partially eliminating the increase in the magnetic force is to implement what is referred to as an immersion stage. In this context, one region of the armature counterpiece engages at least in certain areas in a recess in the magnet armature as soon as the magnet armature undershoots a certain distance from the armature counterpiece. The implementation of such an immersion stage in a solenoid device is, however, complex because very precise guidance of the magnet armature with respect to the armature counterpiece is necessary in order to avoid impacting or contact between the magnet armature and the armature counterpiece, even in the region of the immersion stage and, in particular, in the radial direction. Such contact would lead to a significant reduction in the efficiency of the actuating device which is composed of the magnet armature and armature counterpiece. The precise guidance may be implemented, for example, by precisely fitting the magnet armature into a magnet armature guide, formed for example by a housing of the solenoid device. However, on the other hand, it must also be possible to move the magnet armature as easily as possible, that is to say without a large application of force. As a result, during the manufacture of the solenoid device very small tolerances have to be implemented in order, on the one hand, to permit the immersion stage and, on the other hand, to permit easy movement of the magnet armature. However, this results in high manufacturing costs.